A major proportion of the roofing felts, pipe coatings, roads, sound deadening panels, coating carpet tiles, joint sealing formulations and mopping adhesives applied nowadays are made of modified bituminous compositions, e.g., bituminous compositions comprising a bitumen component and an elastomer component, typically a styrenic block copolymer such as SBS (polystyrene-polybutadiene-polystyrene); SEBS (polystyrene-poly[ethylene-butylene]-polystyrene); SIS (polystyrene-polyisoprene-polystyrene) and SEPS (polystyrene-poly[ethylene-propylene]-polystyrene) and the like. Advantages of modified bituminous compositions over traditional systems (blown bitumen) include: improved fatigue resistance (the accommodation of repeated thermal movements of the roof); improved flexibility (especially at low temperature); improved strength (to allow a reduction in the number of plies of felt by replacing in whole or part the traditional blown bitumen coated system); improved resistance to permanent deformation, puncture and tear; and improved elasticity, resulting in a greater capacity to bridge movement of crack and joints.
Styrenic block copolymers of particular interest are SBS type polymers having a relatively high “vinyl” content, i.e., a content of butadiene moiety built into the polymer backbone by 1,2-addition of at least 10 mol % (based on the total butadiene content). These Improved Processing Durability polymers have excellent high temperature viscosities and excellent ageing characteristics in bituminous compositions.
Unfortunately, high vinyl polymers, i.e. IPD polymers (IPD is a trademark) have an increased tendency to cross-link (gelation tendency) when subjected to or stored at elevated temperatures, as compared to ordinary SBS or SEBS type polymers. This is due to the higher vinyl content. For instance, in mapping adhesives and/or other applications requiring high blending temperatures (greater than 200° C.) preferably fully hydrogenated SEBS type polymers are used. They are used despite their higher costs, as SBS type polymers and high vinyl polymers are more vulnerable to cross-linking at the elevated temperatures.
It would therefore be of great interest to find a styrenic block copolymer that combines the high temperature viscosity and aging characteristics of an IPD polymer with the reduced tendency to gelation normally associated with SEBS type polymers.
In addition, it would be of great interest to find a styrenic block copolymer with increased compatibility with various bitumens. Thus, bituminous compositions comprising more than 3% by weight of an ordinary stryenic block copolymer and e.g. a Venuzuelan bitumen may suffer from insufficient storage ability due to phase separation. When phase separation occurs, then the composition is less processable due to substantial viscosity increase in the polymer rich phase.